The present invention generally relates to a head for recording a signal containing a high frequency component as in a television signal, onto a recording medium having a high coercive force or for reproducing such a signal therefrom, and more particularly, to an amorphous magnetic head in which a main core is composed of an amorphous magnetic material and also, to a method of manufacturing such an amorphous magnetic head in an efficient manner.
Generally, in a magnetic head for a video tape recorder (VTR), ferrite single crystal material is employed for a main core, because said material is superior in abrasion resistance, with favorable soft magnetic characteristics. Incidentally, owing to the recent trend toward compact size of video tape recorders, there has been a tendency that a material such as a metal tape and the like having a high coercive force and capable of achieving recording at a higher density is employed also for a magnetic tape, for example, as in the so-called 8 mm movie camera type video tape recorders. Different from the conventional .gamma.-Fe.sub.2 O.sub.3 tape, such metal tapes have a high coercive force, and therefore, if ferrite materials having saturation flux densities in the range of 4000 to 5000 gauss at most are adopted, the magnetic head is subjected to magnetic saturation, and can not effect magnetization by overcoming the coercive force of the metal tape. Accordingly, at present, investigations are made into the magnetic heads which employ Fe-Al-Si alloy (sendust) materials (saturation flux density Bs .apprxeq.8000 gauss), amorphous material (saturation flux density Bs .apprxeq.10,000 gauss), etc. having higher saturation flux densities as main cores, of which the sendust heads have already been supplied into the market as audio heads corresponding to metal tapes. However, the sendust heads as referred to above have various disadvantages for the heads of video tape recorders to be used in a higher frequency range (e.g. 5 MHZ or thereabout) in that machining thereof is difficult, while due to a low electrical resistance as compared with the ferrite material, the sendust heads have a large eddy current loss at high frequency range, with a sharp reduction of the effective permeability, and thus, the sendust heads have not been supplied as yet into the market for the heads of video tape recorders currently available.
On the other hand, with respect to the amorphous magnetic head, although attention has recently been directed to the amorphous material itself (during the past five years at most) as a future magnetic material for development both in Japan and abroad, the amorphous magnetic heads have not yet been put into practical application at the current stage.
As is well known, the amorphous material is obtained by a manufacturing method referred to as a liquid melt rapid cooling method, in which an amorphous material having an alloy composition not conceivable by the conventional knowledge of metallurgy may be produced in terms of principle. On the contrary, there is a limitation to the configurations of the material to be produced by the above manufacturing method. More specifically, since it is required to rapidly cool the molten metal at cooling speeds of 100,000.degree. to 1,000,000.degree. C./sec., the resultant amorphous material is obtainable only in the form of a ribbon-like sheet of 10 to 100 microns in thickness or in the form of a powder.
Accordingly, in the amorphous magnetic material, it is not possible to employ, as it is, the manufacturing method conventionally adopted for the ferrite material, i.e., the processing technique such as cutting, polishing, welding, etc. from a bulk material. However, in the case where the conventional manufacturing method as described above is to be followed somehow, it may be considered to employ a starting material prepared by laminating a large number of ribbon-like sheets one upon another (i.e., forming such ribbon-like sheets into a shape, similar to the bulk material), thereby to constitute a magnetic head with a track width less than a thickness of the ribbon-like sheet, but since precise control of a thickness of a bonding material layer between the ribbon-like sheets can not be readily effected, it is extremely difficult to arrange the confronting core halves to face each other precisely.
Moreover, as a problem inherent in the amorphous material, there is the problem related to crystallization temperature Tx. Generally, amorphous materials prepared by the rapid cooling method have transition points of crystalline structure referred to as vitrification temperature Tg and cyrstallization temperature Tx. In connection with the above, the vitrification temperature is a temperature at which the amorphous material begins to be softened in the similar manner as in the common soda-lime glass, silica glass, etc., while the crystallization temperature is a temperature at which the amorphous structure is transferred to the crystalline structure. It is to be noted here that, different from glass in general, the amorphous material is not provided with reversibility during passing of the above transition points. In other words, once the amorphous structure has been turned into the crystalline structure, it will never be returned into the original amorphous state. Accordingly, for manufacturing magnetic heads with the use of such amorphous material as described above, it is not possible to apply thermal or mechanical energy exceeding the crystallization temperature Tx, while processing techniques such as glass welding, brazing, etc. for the conventional ferrite material, sendust material, etc. can not be applied, thus making it necessary to develop new processing and manufacturing techniques.